Electric vehicles (HEV, PHEV, BEV, etc.) use electricity as main power or auxiliary power. For this purpose, a battery pack for a vehicle including a plurality of battery cells is mounted in the vehicle. Since the battery pack for the vehicle has a very high voltage, as disclosed in the following Patent Document 1, a positive electrode terminal of the battery pack for the vehicle is connected to a positive electrode contactor (or a positive electrode relay), a precharge circuit is connected to the positive electrode contactor in parallel, and a negative electrode terminal of the battery pack for the vehicle is connected to a negative electrode contactor (or a negative electrode relay), thereby securing stability of the vehicle.
However, the relays of the vehicle connected to the battery pack for the vehicle may be fused due to a high current supplied from the battery pack, and thus may fail to operate properly. When the relays for the vehicle are in a fused state or in an inoperative state as described above, the possibility of explosion of the battery pack and an electric shock of a driver becomes high, which may cause danger to both the vehicle and the driver.
Accordingly, the following Patent Document 1 discloses that the fusion of the contactors can be detected by detecting a change in a leakage current state by an on/off of a precharge relay with a leakage detection circuit.